Mostly the oceans are cold, dark and have extremely high pressure. Except at the very top, they are completely inhospitable to humans. Even this humpback whale can only dive to about 700 feet, so there's a lot about the ocean it doesn't know. Earth would not be the same planet without its oceans.

Oceans Moderate Climate

The oceans, along with the atmosphere, keep temperatures fairly constant worldwide. While some places on Earth get as cold as -70
o
C and others as hot as 55
o
C, the range is only 125
o
C. On Mercury temperatures go from -180
o
C to 430
o
C, a range of 610
o
C.

The oceans, along with the atmosphere, distribute heat around the planet. The oceans absorb heat near the Equator and then move that solar energy to more polar regions. The oceans also moderate climate within a region. At the same latitude, the temperature range is smaller in lands nearer the oceans than away from the oceans. Summer temperatures are not as hot, and winter temperatures are not as cold, because water takes a long time to heat up or cool down.

The oceans are an essential part of Earth’s water cycle. Since they cover so much of the planet, most evaporation comes from oceans and most precipitation falls on oceans.

Biologically Rich

The oceans are home to an enormous amount of life. That is, they have tremendous biodiversity (
Figure
below
). Tiny ocean plants, called phytoplankton, create the base of a food web that supports all sorts of life forms. Marine life makes up the majority of all biomass on Earth. (
Biomass
is the total mass of living organisms in a given area.) These organisms supply us with food and even the oxygen created by marine plants.

Polar bears are well adapted to frigid Arctic waters.

Summary

Oceans moderate Earth's temperature by not changing temperature rapidly and by distributing heat around the planet.

Oceans are an enormous reservoir for water in the water cycle.

Oceans have tremendous biodiversity and the majority of all biomass on Earth.